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A veteran off-duty San Diego police officer using an ATM in Escondido was shot and seriously injured after a suspect attempted to rob him, police said.

Sources tell NBC 7 that at least one suspect made Officer Les Stewart lay face down at the ATM machine just after noon Monday.

The suspect went through Stewart's wallet and saw his Police Department badge inside, then took his wallet and cell phone and shot him in the head "execution-style."

Stewart was using the ATM at the San Diego County Credit Union on South Escondido Boulevard when the suspect approached him, took his cash and wallet and then shot him, according to the Escondido Police Department.

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Stewart is a 27-year veteran with the San Diego Police Department. He is 57 years old, and was set to retire in December, the sources said.

Several employees at the credit union pulled the officer in and locked the door immediately after the shooting, according to Lt. Craig Carter with the EPD.

Stewart was shot in the back of the head and sustained serious injuries, Carter said.

Carter added that the bullet grazed the officer's skull. He is now in guarded watch at Palomar Hospital. The bullet only grazed the top of the officer's head, leaving a three inch-long wound that took about six staples to close, sources told NBC 7.

Stewart's wife arrived at the hospital Monday evening to be with him. Several high ranking San Diego Police officers have been stopping by to give their support, including SDPD Chief William Lansdowne.

The suspect is still at large. Police describe him as a male between the ages of 25 to 40 years old, 5-foot-7, stocky build, wearing a black button up long-sleeved shirt, black pants, a black wind breaker-type jacket and a black baseball cap with the word POLICE in white lettering.

The suspect fled on foot, heading south on Escondido Boulevard toward Felicita Avenue. Authorities are searching for him on ground in the Sheriff's Department ASTREA helicopter.

Meanwhile, authorities are also looking into whether this incident is related to a carjacking in this Sam's Club parking lot in Mission Valley.

A victim told police he was approached by a man and woman. The two suspects set their white Crown Victoria (right) on fire and then allegedly stole the victim's Suzuki hatchback.

Chula Vista Police also say that a suspicious car fire reported later Monday evening may be related to the shooting. Residents in a Chula Vista Cul-de-Sac saw a black Suzuki hatchback burning and put it out with a fire extinguisher.

Police are investigating the car to determine who the driver is or any possible suspects.

The suspect in that case was also dressed in all black clothing.

Police are still investigating the scene. Check back for updates on this developing story.